Automotive coatings are subject to various physical stresses. One of these stresses is the severe and sudden impact caused when stones or gravel from the road surface hit the painted surface of the vehicle, causing the coating to chip, known in the art as stone chipping.
It is known in the automotive industry to apply primer coatings and anti-chip coatings to areas of a vehicle which are prone to stone chipping. Coatings for this purpose have conventionally been unsaturated polyester based coatings and acrylic based coatings. Acrylic based primer and anti-chip coatings are desirable because they provide a hard coating and a primer layer that is resistant to degradation by ultraviolet radiation. UV radiation causes intercoat degradation of the primer layer, which causes a loss of adhesion between the primer coating and other coating layers and results in delamination. However, the use of hard acrylic coatings is problematic, as acrylic based coatings also tend to be more brittle and less chip resistant than polyester systems.
The present invention is directed to improving the resistance of the coating to chipping upon contact with stones or gravel. It has been discovered that a powder coating including both a polyurethane resin and an acrylic resin provides a coating with increased flexibility and greatly improved resistance to stone chipping.
The coating may be used alone or over electrocoat, an as a primer in a multi-coat system, where the primer is applied over electrocoat and basecoat and topcoat are applied over the primer coating layer.